Pneumatic detector

A pneumatic detector consists of a small cylindrical chamber that is filled with xenon and contains a blackened membrane to absorb infrared radiation and heat the gas. One end of the cylinder is sealed with a window that is transparent to infrared radiation the other end is sealed with a flexible diaphragm that moves in and out as the gas pressure changes with cooling or heating. The temperature is determined from the position of the diaphragm. 

Pneumatic detector A heat detector that is based on changes in the pressure that a gas exerts on a flexible diaphragm. p-ii junction diode A semiconductor device containing a junction between electron-rich and electron-deficient regions permits current in one direction only. 

Although these various types of pneumatic detector seem awkward compared with modern solid state devices, their importance should not be underestimated. The Golay cell is still the basic detector used in a large amount... 

A specific gravity meter uses a pneumatic detector and the nitric acid concentration meter is an electrodeless conductivity meter. Eight-inch-long, one-lnch-diameter BF, detectors and incline Nal gamma monitprs are used routinely as process and waste stream and Unk monitors. 

Chevrier J-B, Baert K, Slater T, Verbist A (1995) Micromachined infrared pneumatic detector for gas sensor. Microsyst Technol 1 71-74... 

Pneumatic detector (Golay cell) IR irradiated membrane heats a cavity filled with gas and changes its volume... 

Pneumatic Detectors. The third type of detector which has been used in infrared spectrophotometers is the pneumatic detector, which is an extremely sensitive gas thermometer. The radiation which reaches the sensitive element or receiver heats the enclosed gas. The resulting small rise in pressure is converted to an electrical signal by one of several possible methods. The most commonly applied version of a pneumatic detector is the Golay cell, whose receiver is an aluminum-coated plastic. In this case the receiver does not necessarily depend on a black coating... 

As previously indicated, most of the spectrophotometers used for analytical purposes are double-beam instruments, and most of these are of the optical null type. A few are in the ratio-recording category. Almost all utilize thermal detectors, either thermocouples or metal bolometers, although some incorporate a Golay pneumatic detector over part or all of their spectral range. Sources employed by commercial instruments run the gamut of all the sources described previously. 

Another temperature to voltage conversion mechanism, used in pneumatic detectors, is based on the gas thermometer. The best known representative of this type of detector is the Golay cell. The infrared absorber is imbedded in a small volume of gas contained in a sealed cell. Radiation heats the absorber and the surrounding gas. The associated increase in pressure causes a small displacement of a thin membrane. In the Golay cell this displacement is sensed by the deflection of an external light beam and registered by an appropriate detector (Golay 1947 ... 

Hickey Daniels, 1969). In a more recent version of a pneumatic detector, the displacement of the membrane is sensed electrostatically as in a condenser microphone (Chatanier Gauffre, 1971). Good pneumatic detectors have obtained NEP values of 2 to 3 X 10 W Hz 5. Golay cells are still in use in many laboratory spectrometers, but have not been applied to space-borne observations, probably because of their weight, complexity, and lower reliability compared to thermopiles and pyroelectric detectors, which are discussed next. 

Golay (1947a) Theoretical Consideration in Heat and Infra-Red Detection, with Particular Reference to the Pneumatic Detector by M. J. E. Golay, Rev. Sci. Instrum. 18, 347-356. 

Schuman (1965) Sensitivity of a Selective Pneumatic Detector by M. Schuman, Appl. Opt. 4,1442. 

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